Radiation-sensitive elements and their preparation



United States Patent 3,249,440 RADIATION-SENSITIVE ELEMENTS AND THEIR PREPARATION Heman Dowd Hunt, Eatontown, N..l., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL,

' a corporation of Delaware No Drawing. Filed Mar. 15, 1963, Ser. No. 265,364 Claims. (Cl. 96-108) This invention relates to new, light-developable, direct writing, radiation-sensitive emulsions, emulsion layers and elements having good sensitivity to a high intensity beam of light or other electromagnetic radiation. The invention also relates to a process of manufacturing such direct writing radiation-sensitive elements.

Radiation sensitive elements adapted for light-recording, e.g., oscillographic recording are known. Such materials comprise both the developing-out type and the printout type. The developing-out type, as the name implies, requires that the photographically exposed material be chemically developed, fixed and washed in order to produce a visible image which is stable against fading or other changes.

The print-out material requires no chemical development step to produce a visible image and may or may not be fixed to provide an image which is not subject to fading or other deterioration. Such materials are generally slower than those materials used in developing-out processes and have poor image permanency.

A third type of radiation-sensitive material especially suitable for light printing and oscillographic recording comprises a silver halide emulsion layer which, when exposed to a high intensity source of radiation, forms a latent image which can then be developed by exposure to difiuse daylight or artificial light of lower intensity. Such materials are fasterthan the print-out materials described above and require no chemical processing; and, therefore, they aiford considerable advantage in doing away with liquid solutions and the necessary processing equipment. It may be desirable, however, because of image fading under extended periods of exposure to ambient light, to chemically process the image for permanent retention of the image record. It is this third type of printing material with which the present invention is concerned.

The prior art suggests for this third type of directprinting material, silver bromide emulsions which have incorporated therein, sulfur-containing compounds such as halogen acceptors, e.g., thiourea, thiosemicarbazides,

etc. The background and image densities of layers comprising such emulsions, however, are not sufficiently stable to permit rapid access to, or prolonged examination of, the recorded images, particularly under conditions of daylight or normal room lighting. -It has also been proposed to make photosensitive emulsions for direct-printing or writing by introducing silver thiocyanate into a silver bromide emulsion. The sensitivity of this material is alleged to be considerably greater than pure silver bromide emulsions containing halogen acceptors of the above type and can be further increased by the use of such compounds. Stability of image and background is also a problem with this latter material. Upon prolonged exposure to ordinary illumination, the background darkens and the image regresses, depending on the exposure conditions, which reduces the ratio between background and image densities. There may also be conditions under which both image and background densities are reduced. Also, where the development radiation contains a high proportion of ultraviolet light, subsequent exposure after light development causes an increase in background density and rapid regression of the light-developed image. It is necessary to resort to bathing the light-developed image in a liquid developing bath containing a silver halide solvent to intensify the image density and preserve or 3,249,440 Patented May 3, 1966 increase the contrast or ratio of background to image density of the originally light-developed image. Treatment in a fixing bath is also recommended for the same purpose.

An object of this invention is to provide new and improved direct writing, radiation-sensitive emulsions, emulsion layers, and elements, e.g., films and papers. Another object is to produce a direct-writing photosensitive element having improved sensitometric characteristics in terms of higher speed and maximum density. A further object is to provide direct writing photosensitive elements which do not require the presence of powerful reducers and restrainers. A further object is to provide photosensitive elements, which may be coated over a wide pH range. A still further object is to provide a direct-writing photosensitive element having good aging stability and consequently increased shelf life. A still further object is to provide a direct-writing photosensitive element which may be developed in conventional developers commercially-available in the photographic field. A still further object of this invention is to provide a process for preparing new photosensitive emulsions for direct writing photosensitive elements for use in making oscillograph recordings, electrocardiograms, seismographs, etc.

It has been discovered that by admixing (1) an emulsion of light-sensitive silver halide grains having an average particle size in the range of 0.1 to 10.0 microns in its greatest diameter and a water-permeable macromolecular organic colloid binder, and (2) molecular iodine '(I in an amount from about 0.26 mol percent to 15 mol percent, preferably from 0.8 mol percent to 10 mol percent, based on the silver halide, said molecular iodine being the only energetic halogen acceptor present in amounts greater than 011 mol percent also based on the silver halide, a light-developable, direct-writing silver halide emulsion having high maximum density and image stability will be obtained. If the emulsion is of the lightdevelopable, direct-writing type, by reason of its constitution apart from the molecular iodine, the addition of such iodine improves the maximum density and image stability. In the process, at least one water-soluble halide taken from the group consisting of lithium, sodium, potassium, calcium, magnesium and ammonium chloride, bromide and iodide (preferrably potassium bromide) are present in the final emulsion in an amount in excess of that necessary initially to precipitate all of the silver as silver halide. The light-developable, direct-writing, radiation-sensitive compositions of this invention comprise an aqueous emulsion or dispersion of light-sensitive silver halide grains having average particle size in the range of 0.1-10 microns in a water-permeable, organic macromolecular colloid having protective colloid properties for silver halide grains, said dispersion containing from about 0.26 mol percent to 15 mol percent and preferably from about 0.8 mol percent to 10 mol percent of molecular iodine (I based on the silver halide, said molecular iodine being the only energetic halogen accepter present in amounts greater than 0.1 mol percent based on the silver halide. The photographic elements of the invention comprise a flexible support, e.g., paper or an organic polymer film having on at least one surface a layer of one of the foregoing colloidal compositions, which has been dried in a conventional manner.

The photographic silver halide emulsions with which .the molecular iodine is incorporated, preferably, are the manner.

The invention, of course, is not limited to the use of silver nitrate as the water-soluble silver salt used to precipitate silver halide. Thus, in place of aqueous silver nitrate, one can substitute another water-soluble silver salt, for example, silver sulfate, silver sulfamate, silver citrate, silver acetate or a mixture of two, three or more of such salts. Among the useful water-soluble inorganic halides which can be used to precipitate the silver halide are those listed above. Mixtures of two, three or more of these can be used to make mixed silver halides.

After precipitation and ripening, the emulsion may or may not be, but preferably is, washed in the manner described in assignees Moede US. Patent 2,772,165. The emulsion isredispersed and digested in the conventional At this point or prior to digestion, optical sensitizing dyes may, if desired, be added to increase the spectral response of the emulsion layer for use in instruments employing a variety of light sources. During this operation from 0.26 to 15 mole percent of molecular iodine based on the silver halide is added. A plumbous salt may also be added as described, in assignees H-unt US. Patent 3,033,682. After the digestion step, the usual coating additions, e.g., hardener, wetting agents, etc. are added and the viscosity is adjusted, as desired by the addition of a further amount of gelatin or other colloid. In general, the ratio of gelatin to silver halide is 2:1, however, this is not at all critical. The prepared emulsion is then coated on a suitable support, e.g., paper and dried to give a dry coating weight equivalent to about mg. AgBr/dm.

To determine the sensitometric characteristics of the material it may be exposed through a 2 step wedge in an electronic flash sensitometer similar to that described by Wyckotf and Edgerton, Journal of the Society of Motion Picture and Television Engineers, 66, 474 (1957). This instrument uses a xenon discharge tube as the source of radiation and has available two exposure times of 10 and 1000 microseconds. Relative sensitivities of materials measured with this instrument can be expressed as the number of steps recorded in the image The exposed material may be photo-developed by irradiation by exposure to room lighting or with light from a fluorescent black light tube at about 75 meter-candles intensity. The images became easily visible in approximately 0.1 to 15 seconds although longer times may be used. To determine the densitiesof the image and background, a reflection densi-tometer may be used whose values correspond to visual density. To test the stability of the background the light-developed image record is exposed to room light at meter-candles continuously for 16 hours. Speed in oscillography is measured in inches per secondv and is called writing speed. The radiation source in a typical instrument designed for the above direct-writing papers is the Osram super high pressure are lamp Type HBO 107/ 1. Writing speeds are determined from the frequency of the signal and the peak to peak amplitude of the oscillation as recorded on the paper.

In order to more specifically illustrate the features of this invention, the following examples are set forth below.

They are not intended to limit the scope of the invention except as set forth in the claims.

Example I A gelatino-silver halide emulsion was prepared by slowly adding an aqueous solution of silver nitrate to an aqueous gelatin solution of potassium chloride in sucha manner that there was mole percent of chloride ion based on silver nitrate. The resulting mixture was ripened for 30 minutes at 140 F. Potassium bromide, in an amount sufficient to provide mole percent based on silver, was then added and ripening continued for an additional 10 minutes. The mixture was then coagulated and washed in the manner described in Example I of Moede, US. Patent 2,772,165. The coagulum was redispersed in an-aqueous gelatin solution containing 4 mole percent of potassium bromide based on the silver. The pH was adjusted to 5 and the emulsion washeld at F. for 5 minutes during which potassium iodide was added in an amount of 10 mole percent based on the silver. The emulsion wasthen divided into three portions, one of which served as a control. To the other two portions, there was stirred in 4.7 and 10.3 mole percent of molecular iodine, respectively. Bulking gelatin was added and the emulsion was digested for 10 minutes at 130 F. Conventional coating aids such as chrome alum for hardening and saponin were then added.v The three portions were coated to give a coating weight of about 30 mg. AgBr/dm. The coated emulsions were dried in a conventional manner.

Samples of the three coated elements were given a 1000 microsecond exposure in the flash tube sensitometer de- Exposure in Flash Sensitonieter 10- Sec. Heated 5 sec. at 400 F. developed 5 see. with photofluod lamp Mole percent I based on AgX 1O- See-Photodeveloped 30 min. with fiu0 rescent lamp 1/2 steps visible Sample No.

Speed D max. Fog

1 Control were r-wm Example ll iodide was added at digestion. The following results were obtained.

Sample N 0.

Exposure in Flash Sensitometer 10- See. Photodeveloped 30 min. with fluorescent lamp 10- Sec. Photodeveloped 30 min. with fluqrescent lamp v2 steps visible 10- Sec. Heated 5 sec. at 400 F. developed 5 sec. photoflood lamp Mole per- D max. Speed D max. Fog

. It appears from thhe above results that although higher amounts than those used in Example I can be used, no substantial beneficial results are obtained using amounts over 1.5 mole percent of molecular iodine.

minutes. During this period, 4.7 mole percent of molecular iodine and 1 mole percent of plumbous nitrate were added with stirring. The emulsion was divided into four portions and to each of them varying quantities of E l "I 5 potassium bromide were added to give the mole percent xamp e excess based on silver halide as indicated in the table The preparation of an emulsion was carried out below. The emulsions were coated, dried and exposed through the coagulation, washing and redispersion stages in the manner described in Example I and gave the folof Example I. The temperature of the redispersion was lowing sensitometric results:

Exposure in Flash Sensitometer 10' See. Photo- 10- See. Photo- 10- Sec. Heated Mole developed min. developed 30 min. 5 see. at 450 F. de- Sample No. Percent with fluorescent with fluorescent vel0ped5sec.photo- KBr lamp lamp V2 steps flood lamp visible D max. Fog Speed D max. Fog

raised to F. and held for 15 minutes. During this Example V time the emulsion was divided into four portions and to each portion there was added with stirring 2.36 mole percent of molecular iodine. To two portions there was added 5 mole percent of potassium iodide and to two por-. tions there was added 1 mole percent of plumbous nitrate as indicated in the table'below. The operations of coating and exposing were carried out as described in Example I with the following results:

Example I was repeated except that the emulsion was ripened at F. and contained 2.6 mole percent of molecular iodine. The emulsion was divided into two portions and the pH of each portion Was adjusted in a conventional manner, e.g., using acetic acid or sodium hydroxide, as indicated in the following table. The emulsions were coated, dried and exposed as described Exposure in Flash Sensitometer Mole percent 10- See. Photo- 10- Sec. Photo- 10- Sec. Heated Sample developed 30 min. developed 30 min. 5 see. at 400 F. No. with fluorescent with fluorescent developed 5 sec. lamp lamp \/2 steps photoflood lamp visible KI Pb (N0 D max. Fog Speed D max. Fog

o o 0. 71 0.38 12 0. 49 0. 15 0 1 0. 72 0. 33 13 0. 50 0. 13 5 0 0. 68 0. 32 12 0. 53 0. l6 5 1 0. 67 0. 30 13 0. 52 0. 17

Example 1V above. The following sensitometric results Were ob- An emulsion was prepared as described in Example I tained.

through the coagulation washing and redispersion stages. At this point, the temperature was raised and held for It will be noted that good results are obtained over a wide p H range.

7 Example VI Unexposed samples from Example'II were exposed and without photodevelopment were processed by developing them for 1% minutes in a developer having the formula:

Grams Metol 1.5 Hydroquinone 6.0 Sodium sulfite (anhydrous) 19.5 Sodium carbonate (anhydrous) 28.0 Potassium bromide 0.8

Water to make 1.0 liter.

The developed elements were rinsed and then immersed for 5 minutes in a fixing solution having the following composition. V

Sodium thiosulfate grams 240 Sodium sulfite (anhydrous) do Acetic acid, 28% ml 47 Potassium aluminum sulfate grams 15 Water to make 1 liter.

The resulting images had a stable image density of 1.0

and a stable background density of .07. The processed element was quite suitable as a permanent record and could be reproduced by conventional ofiice copy equipment.

Example VII Example I was repeated except that just before digestion there was added 0.16 gram of 3,3-diethyl-5,5'-diphenyl- 9-methyl benzoxacarbocyanine iodide per mole of silver bromide. This impartedsensitization to the emulsion in the green region of the spectrum and provideda photo-' Where it is desired, other halides or combination of halides may be used to form the silver halide grains. For example, pure silver chloride, chlorobromide or iodobromide may be used. Where soluble chloride salts are used his desirable, because of solubility differences, to form the silver halide grains of desired composition and size and then add sufiicient soluble bromide salts to provide the desired concentration of bromide ions.

In place of the gelatin binding agent used in the foregoing examples there can be substituted synthetic water-- permeable organic colloid binding agents. Such agents include water-soluble or permeable polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers, and acetals containing a large number of extralinear -CH CHOH- groups; hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds, for example maleic anhydride, acrylic and methacrylic acid esters and styrene. Suitable colloids of the last mentioned type are disclosed in US. Patents 2,276,322; 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include the polyvinyl lactams of Bolton US. Patent 2,495 918, e.g., poly-N-vinylpyrrolidone; the hydrophilic copolymers of N-acrylamido alkyl betaines in Shacklett US.

Patent 2,833,650 and hydrophilic cellulose ethers and esters.

Suitable supports for the novel photographic emulsions of this invention include those used in the prior art for light-writing and oscillographic recording. The preferred support: is photographic grade paper but may be of any material suitable for coating photographic emulsions such as cellulose ester films and the film base materials disclosed in Alles et al. US. Patent 2,627,088 and Alles US. Patent 2,779,684 and polystyrene. Where paper is used brightening agents of the triazinyl stilbene type compounds may be incorporated either in the emulsions or in the papers.

The novel feature of incorporating molecular iodine into a silver halide emulsion after the precipitation stage either with or without additional lead salts and with or without the addition of excess bromide ions produces lightdevelopable, direct-writing, photosensitive emulsion layers having certain advantages over the prior art products. In addition to being extremely convenient to use because wet processing can be eliminated, it is also adaptable to couventional chemical development where it is desired. The invention also provides an elementwherein one may subject the exposed material to relatively high illumination for long periods of time or use the material to photographically reproduce the image record using high intensity exposing radiation without serious image deterioration. The elements of this invention have high photographic speed and permit rapid access to the recorded image. They also provide images having high maximum density and image stability. The elements of this invention may also be processed in the manner disclosed assignees Hunt patents referred to above and in Hunt applications U.S. Serial No. 137,534, filed September 12, 1961 (Patent No. 3,183,088, May 11, 1965), and US. Serial No. 152,914, filed November 16, 1961. This invention also provides direct-writing photosensitive elements having good aging stability. Still further advantages will be apparent from the foregoing description.

I claim:

1. A photographic element comprising a support and a radiation-sensitive, direct-writing, light-developable layer comprising an admixture .of (1) an emulsion of lightsensitive silver halide grains having anaverage particle size in the range of 0.1 to 10.0 microns in its greatest diameter and a water-permeable macromolecular organic colloid binder, and (2') molecular iodine (I in an amount from about 0.26 mol percent to 15.0 mol percent, said molecular iodine being the only, energetic halogen acceptor present in amounts greater than 0.1 mol percent, the mol percentages being based on the silver halide.

2. An element according to claim 1 wherein said eolloid binder is gelatin.

3. An element according to claim 1 wherein said silver halide is silver bromochloride and said emulsion contains a plumbous salt.

4. An element according to claim 1 wherein (3) a water soluble halide ispresent in an amount suflicient to provide bromide ions in excess of those necessary initially to precipitate all of the silver ions as silver halide.

5. An element according to claim 1 wherein (3) a water soluble bromide is present in an amount sufiicient to provide bromide ions in excess of those necessary initially to precipitate all of the silver ions assilver bromide.

References Cited by the Examiner UNITED STATES PATENTS 1,730,505 10/1929 Hart 96-1 3,033,682 5/1962 Hunt 96-119 3,047,392 7/1962 Scott 96-119 3,109,737 11/1963 Scott 96-119 NORMAN G. TORCHIN, Primary Examiner.

A. E. TANENHOLTZ, Examiner.

J. RAUBITSCHEK, Assistant Examiner. 

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND A RADIATION-SENSITIVE, DIRECT-WRITING, LIGHT-DEVELOPABLE LAYER COMPRISING AN ADMIXTURE OF (1) AN EMULSION OF LIGHTSENSITIVE SILVER HALIDE GRAINS HAVING AN AVERAGE PARTICLE SIZE IN THE RANGE OF 0.1 TO 10.0 MICRONS IN ITS GREATEST DIAMETER AND A WATER-PERMEABLE MACROMOLECULAR ORGANIC COLLOID BINDER, AND (2) MOLECULAR IODINE (I2) IN AN AMOUNT FROM ABOUT 0.26 MOL PERCENT TO 15.0 MOL PERCENT, SAID MOLECULAR IODINE BEING THE ONLY ENERGETIC HALOGEN ACCEPTOR PRESENT IN AMOUNTS GREATER THAN 0.1 MOL PERCENT, THE MOL PERCENTAGES BEING BASED ON THE SILVER HALIDE.
 4. AN ELEMENT ACCORDING TO CLAIM 1 WHEREIN (3) A WATER SOLUBLE HALIDE IS PRESENT IN AN AMOUNT SUFFICIENT TO PROVIDE BROMIDE IONS IN EXCESS OF THOSE NECESSARY INITIALLY TO PRECIPITATE ALL OF THE SILVER IONS AS SILVER HALIDE. 